Helicopter cyclic and collective pitch mechanism

ABSTRACT

An apparatus for changing both the cyclic and collective pitch of each blade of a rigid rotor helicopter with a single differential gear mechanism. To change the collective pitch, a spider element is moved up or down which simultaneously actuates the differential gear mechanism for each blade in order to change its pitch collectively To change the cyclic pitch, a seesaw type linkage is actuated and applies a torque to the swash plate and control gyro of the helicopter. The control gyro supports lateral arms and the applied torque changes their plane of rotation. Linkages connected between each of the control arms and differential gear mechanisms react to this change in the plane of rotation and actuate the appropriate differential gear mechanisms to cyclically change the pitch of the blades.

United States Patent Scheibe et al.

[ Oct. 24, 1972 [54] HELICOPTER CYCLIC AND 3,027,948 4/ 1962 Goland etal. ..416/ 18 COLLECTIVE PITCH MECHANISM 3,232,348 1/ 1966 Jarosch..416/1 14 X [72] lnventors: Harold R. Scheibe, King George; 3 John E-Blankenship,

Fredfincksburg both of Primary ExaminerEverette A. Powell, Jr. [73]Assignee: The United States of America as Att0rneyR. S. Sciascia andThomas 0. Watson, Jr.

represented by the Secretary of the Navy [57] ABSTRACT [22] Filed: Feb.3,1971 An apparatus for changing both the cyclic and collective pitch ofeach blade of a rigid rotor helicopter with [211 App! "L161 a singledifferential gear mechanism. To change the collective pitch, a spiderelement is moved up or down 52 us. c1 ..416/114, 416/160 whiehSimultaneously aetuetes the differential gear 51] Int. c1.....-.....B64c 27/74 mechanism for eeeh blade in Order to ehange its Pitch [58Field of Search ..416/18, 24, 98, 114, 160 collectively To Change theeyelie pitch, a seesaw yp linkage is actuated and applies a torque tothe swash [56] References Cited plate and control gyro of thehelicopter. The control 1 gyro supports lateral arms and the appliedtorque UNITED STATES PATENTS changes their plane of rotation. Linkagesconnected between each of the control arms and differential gear2,491,260 12/1949 Green ..416/98 mechanisms react to this change in theplane of rota 2,519,762 8/1950 Hoffmann et a1 ..416/18 tion and actuatethe appropriate differential gear Avery X ec anis to cyc c y Ch g e o te 2,648,387 8/1953 Doman ..416/160 X blades 2,818,123 12/1957 Hlller..416/24 2,827,968 3/1958 Sissingh et a1. ..416/18 5 Claims, 2 DrawingFigures PATEMTEDnm 24 I972 SHEET 1 OF 2 INVENTORS SUHE/BE, JR. BLA/VKE/V5H/P mafia. 0 6411 HAROLD 1?. JOHN E.

PATENTED B 2 39700 350 sum 2 or 2 FIG. 2

HELICOPTER CYCLIC AND COLLECTIVE PITCH MECHANISM STATEMENT OF GOVERNMENTINTEREST The invention described herein may be manufac tured and used byor for the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The present invention relates generally toimprovements in rigid rotor helicopters, and more particularly itpertains to new and improved rotor control means wherein a singledifferential gear mechanism changes both the cyclic and collective pitchof a blade of a rigid rotor helicopter.

In the field of helicopter rotor controls, it has been the generalpractice to obtain cyclic pitch of the rotor blades by connecting ahorizontal link to the leading edge of a rotor blade and extending avertical or inclined link downwardly from a control gyro arm to thehorizontal link. In operation, when the gyro is tilted down toward arotor blade, it decreases the blade angle of attack and vice versa. Thissystem, though simple, has been unsatisfactory in that it provides onlylimited ratios between the control gyro tilt angle and the change in theblade angle of attack. In the prior art, it has also been the generalpractice to obtain collective pitch by changing the distance between theplane of the rotor blades and the control gyro hub, usually by movingthe control gyro until the desired change in angle of attack has beenbrought about. However, this system has also been unsatisfactory in thatit requires overcoming the mass of the control gyro and it also requiresthe use of a spline attached to the blade hub which can slide throughthe gyro hub. Both of these conditions require a large control system toassure adequate response and to overcome friction.

OBJECTS OF THE INVENTION Accordingly, it is an object of the presentinvention to provide an apparatus for introducing both cyclic andcollective pitch to a rotor blade from the control gyro platform throughthe use of a single differential gear mechanism.

Another object of the invention is to provide a system whereby virtuallyany linkage ratio can be achieved.

A further object of the invention is to eliminate the need for movingthe massive control gyro and the need for a working spline.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION The general purpose of this invention is toprovide a single differential gear mechanism for each rotor blade thatwill achieve both cyclic and collective pitch in that blade of the rigidrotor helicopter. To change the collective pitch, a motor-driven shaftmoves a spider ele ment up or down to simultaneously actuate thedifferential gear mechanism for each blade in order to change theirpitch collectively. To change the cyclic pitch, a seesaw-type linkage isactuated and applies a torque to the swash plate and control gyro of thehelicopter. The control gyro supports lateral arms and the appliedtorque changes their plane of rotation. Through linkages connected toeach of the lateral control arms, the differential gear mechanism of theappropriate blades are actuated to cyclically change the pitch of theblades. In this manner, the present invention provides a device whichavoids the problem of moving the control gyro to change the pitch of therotor blades.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a typical helicopterrotor control gyro assembly with portions thereof cut away.

FIG. 2 is a detailed perspective view of the differential gear mechanismof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows ahelicopter rotor system 10 of the rigid rotor type wherein four rotorblades 12 are connected to a rotor blade hub 14 through four housings16. Each of the housings 16 contains the differential gear mechanism ofthe present invention which may also be referred to as the cyclic andcollective pitch control mechanism for changing rotor blade pitch.

A control gyro assembly 18 comprises four radially extending cross arms20 (only two shown), each having end weights 22, supported by a controlgyro hub 24. Control gyro hub 24 includes a swash plate 26 and aconstant velocity universal joint 28. Joint 28 is of the type knowncommercially as the Rzeppa Constant Velocity Universal Joint, which ismanufactured by the Dana Corporation of Detroit, Michigan. Two torquemotors (not shown), are provided in a housing 30 and are connected toswash plate 26, so that upon actuation, one of the motors applies atorque to process the control gyro 18 in a north-south direction and theother in an east-west direction. This structure and/or operation isdescribed with greater particularity in a co-pending application, Ser.No. 818,625, in the name of Harold R. Scheibe, filed Apr. 23, ,1969 nowU.S. Pat. No. 3,572,965, and assigned to the assignee of the presentapplication. Mounted on the rotor of each of the torque motors is a rackand pinion arrangement to actuate one end 32 of a seesaw linkage 34which is supported at its middle by pivot support 36. At its other end,is a rod 38 which is connected to swash plate 26. Upon actuation of oneof the torque motors, a torque is applied to the swash plate 26 andcontrol gyro 18 through the rack and pinion and linkage arrangement. Anidentical arrangement (not shown) associated with the other torque motoris provided at the other side of housing 30 and serves to precess thecontrol gyro 18 in a direction orthogonal to the direction of precessioncaused by the first torque motor. The point of application of force tothe swash plate 26 by this other torque motor is displaced from thepoint of application of force by the first torque motor. The controlgyro arms 20, which precess with the control gyro 18, are each slaved tothe helicopter rotor blades 12 by a linkage 40 and a shaft 42 via thedifferential gear mechanism in each housing 16 and a gear reductionsystem in each housing 44 which provides the proper actuating ratios foreach of the blades 12 to achieve cyclic pitch. Collective pitch ischanged by raising or lowering, with respect to blade hub 14, alightweight spider 46, having four fingers, each of which is connectedby a vertical link 48 to the differential gear mechanism in each of thehousings 16. Spider element 46 is connected to -a center shaft 50 whichis actuated by a third motor (not shown) in housing 30.

FIG. 2 shows in detail the differential gear mechanism or cyclic andcollective pitch control mechanism of the present invention which islocated in each of the housings 16. Each mechanism includes a collectivepitch control link 52, each of which is connected to a different one ofthe vertical links 48 and a cyclic pitch control link 54, each of whichis connected to a different one of the linkages 40.

A description of the differential gear mechanism of FIG. 2-will now begiven and it will be applicable to each of the four differential gearmechanisms in the preferred embodiment of FIG. 1, as they are allidentical in structure. Collective pitch control link 52 pivots about anon-rotatable blade shaft 56 on a bearing 58. A shaft 60, which is keyedto cyclic pitch control link 54, rotates in a bearing 62 which is alsomounted within link 52. Shaft 60 is also keyed to a gear 68 to cause itto rotate therewith. Gear 68 engages another gear 70 and causes it torotate about the non-rotatable blade shaft 56 on a bearing 72. As gear70 rotates, it drives a gear 74 which is keyed to the rotatable shaft42. Shaft 42, which rotates in a bearing 76, is rigidly aligned with thenon-rotating blade shaft 56 by a link 78 which is keyed to shaft 56.Rotatable shaft 42 is connected to housing 44 (see FIG. 1) whichcontains a suitable reduction gear mechanism to actuate rotor blades 12.

In operation, collective pitch control is obtained by actuating themotor-driven center shaft 50 to raise or lower lightweight spider 46 andits four fingers with respect to blade hub 14. This movement of spider46 will cause each of the vertical links 48 to actuate the collectivepitch control links 52 within each of the differential gear housings 16.Assume, for explanatory purposes, that the operation of the differentialgear mechanism shown in FIG. 2 is representative. If link 52 is movedupward in the direction of the arrow shown in FIG. 2, it will pivotabout non-rotatable blade shaft 56, due to bearing 58. To vary thecollective pitch, cyclic pitch control link 54 is held fixed by linkage40. The other end of link 54 will then be free to move in a downwarddirection as link 52 pivots abut shaft 56. This downward movement oflink 54 will cause keyed shaft 60 to rotate in bearing 62 and forcekeyed gear 68 to rotate therewith. As gear 68 is actuated, it willrotate meshed gears 70 and 74, thereby causing keyed shaft 42 to rotatein a clockwise direction. Rotation of shaft 42 causes rotor blades 12 tochange pitch collectively through a suitable reduction gear mechanism inhousing 44. In this manner, the angle of attack of blades 12 isincreased which results in increased helicopter lift. To decrease lift,collective pitch control link 52 is moved in a downward direction.

Cyclic pitch control is obtained by actuating one of the two seesawlinkages 34, depending on whether precession in a north-south directionor an east-west direction is desired. Upon actuation, a rod 38 applies atorque to the swash plate 26 and control gyro l8 through the rack andpinion and linkage arrangement described above. As the control gyro 18supports gyro arms 20, the applied torque changes the parallelrelationship between the planes in which rotor blades 12 and controlgyro arms 20 rotate in. This change in the parallel relationship of theplanes will actuate linkages 40 which are connected to the cyclic pitchcontrol links 54 of the differential gear mechanisms, as represented inFIG. 2. To vary the cyclic pitch, collective pitch control link 52 isheld fixed by spider 46 and vertical link 48, as cyclic pitch control 54is actuated by linkage 40. Link 54 may be actuated up or down to pivotabout the axis of shaft 60. If link 54 is actuated upwardly, keyed shaftwill rotate in a clockwise direction and keyed gear 68 will rotatetherewith. As gear 68 is actuated, it will rotate meshed gears 70 and74, thereby causing keyed shaft 42 to rotate in a clockwise direction.Rotation of shaft 42 causes rotor blades 12 to change pitch cyclicallythrough the reduction gear mechanism in housing 44. The force input tothe blades 12 and the difference in aerodynamic lift momentsproducedbetween the advancing and retreating blades causes the rotorplane to precess in the desired direction, which results in movement ofthe helicopter in the desired direction.

To obtain cyclic pitch, the differential gear mechanism operates in thesame manner as described to obtain collective pitch. The only differenceis that for collective pitch, each of the four differential gearmechanisms are actuated the same amount to increase or decreasehelicopter lift, whereas for cyclic pitch each of the four differentialgear mechanisms may be actuated in different amounts in order to causethe helicopter to move in the desired lateral direction or in a forwardor reverse direction.

Accordingly, it is seen how this invention provides a singledifferential gear mechanism to achieve both collective and cyclic pitchmotions in each blade of a rigid rotor helicopter. In so doing, itoffers a simple technique for varying the linkage ratios between thecontrol gyro angle and the angle of attack of the blades and iteliminates the requirement of vertical movement of the control gyro withrespect to the blade axis. It is to be noted, that by varying thelengths of pivot points and gear diameters, virtually any linkage ratiocan be achieved. Further, the invention not only eliminates the need formoving the massive control gyro, but also eliminates the need for aworking spline. Alternative arrangements of gears and ratios may beconsidered to be simple variations of the present invention.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings.

What is claimed is:

1. An apparatus for varying both the collective and cyclic pitch in theblades of a rigid rotor helicopter with a single differential gearmechanism comprising,

a plurality of rotor blades;

an equal plurality of differential gear mechanisms;

each of said differential gear mechanisms including a collective pitchcontrol link having first and second bearings therein;

a non-rotatable blade shaft having one end mounted in the first bearingand its other end connected to a gear reduction means cooperating with arotor blade;

a second shaft mounted in the second bearing having one end keyed to acyclic pitch control link and its other end keyed to a first gear;

a second gear rotatably mounted on said blade shaft and engaging saidfirst gear;

a third link having a third bearing therein, said third link being keyedto said blade shaft between said second gear and said gear reductionmeans;

a rotatable shaft mounted in said third bearing having one end keyed toa third gear, said third gear engaging said second gear, the other endof said rotatable shaft being connected to said gear reduction means;

first means to actuate said collective pitch control link in each ofsaid differential gear mechanisms an equal amount to cause the first,second and third gears to interact, actuating said gear reduction meansto vary the pitch of said rotor blades collectively; and

second means to actuate said cyclic pitch control link in each of saiddifferential gear mechanisms a different amount to cause the first,second and third gears to interact, actuating said gear reduction meansto cyclically vary the pitch of said rotor blades.

2. The apparatus of claim 1 wherein said first means comprises amotor-driven center shaft connected to a spider having a plurality offingers equal in number to the plurality of rotor blades, each of saidfingers having a vertical link thereon cooperating with a collectivepitch control link whereby vertical movement of said center shaft willdisplace said spider and the respective vertical links to simultaneouslymove the collective pitch control link in each of said differential gearmechanisms an equal amount.

3. The apparatus of claim 2 wherein said second means comprises aplurality of motor-driven seesaw linkage means for applying apredetermined torque to a swash plate and control gyro means whichcooperates with the cyclic pitch control link in each of saiddifferential gear mechanisms.

4. The apparatus of claim 1 wherein said second means comprises aplurality of motor-driven seesaw linkage means for applying apredetermined torque to a swash plate and control gyro means whichcooperates with the cyclic pitch control link in each of saiddifferential gear mechanisms.

5. The apparatus of claim 4 wherein said control gyro means includes aplurality of gyro control arms and means for connecting each of saidcontrol arms to a different one of said differential gear mechanisms.

1. An apparatus for varying both the collective and cyclic pitch in theblades of a rigid rotor helicopter with a single differential gearmechanism comprising, a plurality of rotor blades; an equal plurality ofdifferential gear mechanisms; each of said differential gear mechanismsincluding a collective pitch control link having first and secondbearings therein; a non-rotatable blade shaft having one end mounted inthe first bearing and its other end connected to a gear reduction meanscooperating with a rotor blade; a second shaft mounted in the secondbearing having one end keyed to a cyclic pitch control link and itsother end keyed to a first gear; a second gear rotatably mounted on saidblade shaft and engaging said first gear; a third link having a thirdbearing therein, said third link being keyed to said blade shaft betweensaid second gear and said gear reduction means; a rotatable shaftmounted in said third bearing having one end keyed to a third gear, saidthird gear engaging said second gear, the other end of said rotatableshaft being connected to said gear reduction means; first means toactuate said collective pitch control link in each of said differentialgear mechanisms an equal amount to cause the first, second and thirdgears to interact, actuating said gear reduction means to vary the pitchof said rotor blades collectively; and second means to actuate saidcyclic pitch control link in each of said differential gear mechanisms adifferent amount to cause the first, second and third gears to interact,actuating said gear reduction means to cyclically vary the pitch of saidrotor blades.
 2. The apparatus of claim 1 wherein said first meanscomprises a motor-driven center shaft connected to a spider having apLurality of fingers equal in number to the plurality of rotor blades,each of said fingers having a vertical link thereon cooperating with acollective pitch control link whereby vertical movement of said centershaft will displace said spider and the respective vertical links tosimultaneously move the collective pitch control link in each of saiddifferential gear mechanisms an equal amount.
 3. The apparatus of claim2 wherein said second means comprises a plurality of motor-driven seesawlinkage means for applying a predetermined torque to a swash plate andcontrol gyro means which cooperates with the cyclic pitch control linkin each of said differential gear mechanisms.
 4. The apparatus of claim1 wherein said second means comprises a plurality of motor-driven seesawlinkage means for applying a predetermined torque to a swash plate andcontrol gyro means which cooperates with the cyclic pitch control linkin each of said differential gear mechanisms.
 5. The apparatus of claim4 wherein said control gyro means includes a plurality of gyro controlarms and means for connecting each of said control arms to a differentone of said differential gear mechanisms.